Bringing up lower level metal nodes of multi-layered IC devices is necessary for IC device modification or re-routing, as well as being useful for debugging and failure analysis. However, the task of bringing up these lower level metal nodes is often difficult and tedious, especially when desired or target metal nodes or layers are buried under other higher level or non-target metal nodes or layers. As a result, not only are target nodes difficult to access, but also, undesired shorts are difficult to prevent. To further complicate the situation, as the number of metal layers increases, the lower level metal nodes become increasingly thinner, and the node population becomes increasingly more dense. These conditions result in a decreased success rate reaching a desired lower level metal node.
Usually, one of two approaches is used to reach a target metal layer in an IC device. RIE (reactive ion etching) is generally used as a global delayering method. In RIE, a plasma etch normally removes passivation layers and dielectric layers to expose the metal layers of all the transistors in a given device. When attempting to achieve a non-uniform etching in which only desired portions of a device are exposed, over-etch problems may result.
Another method utilizes a FIB (focused ion beam) system. With FIB utilization, individual areas are exposed through the use of a focused ion beam. FIB techniques normally use a low level current, i.e., less than about 1000 picoamperes (pA), to open individual areas, e.g., windows of approximately 15 micron (.mu.m).times.15 .mu.m. Unfortunately, such low levels of current result in significantly long time periods to open the windows, for example, on the order of thirty minutes per window. Further, when the FIB is used for desired nodes in lower levels if the FIB window is not opened wide enough, the depth of the trench formed by etching through the upper layers limits the detection of a signal coming back from the node during e-beam (electron beam) probing. Normally, the desired aspect ratio (ratio of height to width) of the trench is 1:1, which is difficult to achieve in the lower level nodes due to the narrow width and increased depth of the trenches.
Accordingly, what is needed is a method and system for exposing desired nodes at local areas efficiently and accurately. The present invention addresses such a need.